Steam separator and boiling water reactor

Abstract

To provide a reactor in which fluid easily flows.SOLUTION: A reactor 142 comprises a reactor pressure vessel 101, a reactor core 103 provided inside the reactor pressure vessel 101 and with fuel assemblies loaded therein, and a steam separator 105 provided inside the reactor pressure vessel 101 and separating water and steam from fluid 5 consisting of steam and water generated in the reactor core 103. The steam separator 105 comprises an annular channel that pours the fluid 5 from an upper part toward a lower part in its inside and opens at a lower part of the steam separator 105, and openings that drain bubbles in the fluid 5 flowing in the annular channel to the side part of the steam separator 105.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] In a forced circulation boiling water reactor (forced circulation reactor), multiple steam-water separators are installed at the top of the core to separate the steam and water from the fluid containing steam and water generated in the core. In the steam-water separator, a swirling speed is given to the fluid by a swirling blade in a diffuser, and the steam and water are separated by centrifugal force using the difference in gas-liquid density. The separated water descends from the space inside the inner cylinder of the steam-water separator through an annular passage between the inner cylinder and the outer cylinder, is discharged from an outlet below the outer cylinder of the steam-water separator, returns to the downcomer, and is sent to the core again by a recirculation pump. Meanwhile, the separated steam is discharged from the central passage of the steam-water separator to the outside, flows into a steam dryer where moisture is removed, and is then sent to the turbine. As a result, moisture can be removed as much as possible from the steam containing moisture generated in the core, and efficient power generation is realized.

[0002] In a three-stage steam separator used in an advanced boiling water reactor (forced circulation reactor, ABWR), separated water with almost no steam mixed in is discharged from a downward outlet in the annular passage between the first stage inner cylinder and the first stage outer cylinder. Separated water and steam are discharged from outlets provided below the second and third stage outer cylinders from the bottom of the steam separator.

[0003] On the other hand, in a natural circulation type boiling water reactor (natural circulation reactor) that does not use a recirculation pump, a large diameter circular pipe flow path called a chimney is installed at the top of the core. The circulation force due to the density difference between the fluid inside and outside the shroud is increased, and cooling water flows into the core. In a natural circulation reactor, the average quality at the inlet of the steam-water separator is higher than that of the ABWR. In addition, due to the influence of the complex flow in the chimney, the variation in the quality of the two-phase gas-liquid flow at a single steam-water separator inlet is larger than that of the ABWR. When the quality at the steam-water separator inlet is high, that is, when the amount of steam increases, the steam flows into the first stage annular flow path and is discharged from the exhaust port. This increases the carry under (the mass flow rate of steam in the fluid discharged from the exhaust flow path of the steam-water separator). When the carry under increases, a lot of steam is contained in the downcomer outside the shroud, and the fluid density decreases. As a result, there is a risk of a decrease in the natural circulation flow rate and even a decrease in the cooling performance of the reactor core.

[0004] Patent Document 1 describes that "the steam-water separator 6 has a standpipe 7, a diffuser 8, a swirler 9, and three-stage steam-water separation sections 10a to 10c. The diffuser 8 is installed at the upper end of the standpipe 7, and the swirler 9 is installed inside the diffuser 8. The inner cylinder 11a is attached to the upper end of the diffuser 8, and the pick-off ring 13a is attached to the upper end of the inner cylinder 11a. The outer cylinder 12a, which forms a drainage passage 15a between itself and the inner cylinder 11a, is installed on the pick-off ring 13a. An air bubble collection chamber 22 formed at the lower end of the drainage passage 15a is formed between the partition member 21 and the outer cylinder 12a. An annular plate 20 located below the outer cylinder 12a is attached to the outer surface of the pipe 22. An outlet 18a is formed between the annular plate 20 and the lower end of the outer cylinder 12a. Air bubbles separated from the water flowing through the bent section 25 are collected in the air bubble collection chamber 22." [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2009-257770 A Summary of the Invention [Problem to be solved by the invention]

[0006] In the steam-water separator 6 described in Patent Document 1, the fluid containing steam and water flowing downward through the drainage flow passage 15a collides with the annular plate 20 at the lower ends of the inner cylinder 11a and the outer cylinder 12a. The flow direction of the fluid then changes to a lateral direction at the annular plate 20, and is discharged to the side of the outer cylinder 12a (steam-water separator 6) through the discharge port 18a. This results in a significant pressure loss, making it difficult for the fluid to flow. The problem to be solved by the present disclosure is to provide a steam separator and a boiling water reactor in which fluid flows easily. [Means for solving the problem]

[0007] The steam-water separator of the present disclosure includes a standpipe that guides fluid containing steam and water generated in a reactor core from below to above, a diffuser that is connected to an upper end of the standpipe to form a flow passage and expands the flow passage cross-sectional area upward from the flow passage cross-sectional area of ​​the upper end, a cylindrical inner cylinder that communicates with the upper end of the diffuser to form a flow passage, a cylindrical outer cylinder that forms an annular flow passage between the inner cylinder and the inner cylinder and has an outlet that opens downward at a lower end of the annular flow passage, and a diffuser that protrudes into the annular flow passage from at least one surface of the outer cylinder or the inner cylinder. the annular passage is formed in the outer cylinder at least in a portion directly below the protrusion, the annular passage is communicated with the outside of the outer cylinder and the annular passage is opened toward a side of the outer cylinder, an annular plate that closes the upper side of the outer cylinder and has a circular hole with a smaller diameter than the inner cylinder, a pick-off ring that extends cylindrically downward from the inner peripheral edge of the annular plate that forms the circular hole and forms the circular hole as a passage upward on the inner cylinder, and a swirler that is disposed as the axial center of the passage through which the fluid flows in the standpipe. Other solutions will be described later in the description of the embodiment of the invention. Effect of the Invention

[0008] According to the present disclosure, it is possible to provide a steam separator and a boiling water reactor in which fluid flows easily. [Brief description of the drawings]

[0009] [Figure 1] 1 is a vertical cross-sectional view of a schematic structure of a boiling water reactor (natural circulation reactor) according to the present disclosure. [Diagram 2] FIG. 2 is an external view of the steam-water separator of the present disclosure. [Diagram 3] 3 is a vertical sectional view of the steam-water separator shown in FIG. 2. [Figure 4] FIG. 4 is a cross-sectional view taken along line BB in FIGS. 2 and 3. [Diagram 5] 4 is a cross-sectional view taken along line CC in FIG. 2 and FIG. 3. [Figure 6] 3 is a bird's-eye view of the vicinity of an opening of the steam-water separator shown in FIG. 2, as viewed from the outside of the steam-water separator. [Figure 7] FIG. 13 is a diagram for explaining the behavior of a fluid flowing through a first stage annular passage, focusing on a specific bubble in the first stage annular passage. [Figure 8] FIG. 8 is a diagram for explaining the behavior of a fluid flowing through the first stage annular flow passage, and is a diagram showing a state in which the air bubble shown in FIG. 7 flows near the flow rate reduction component. [Figure 9] 8 is a diagram for explaining the behavior of the fluid flowing through the first stage annular flow passage, and is a diagram showing a state when the air bubble shown in FIG. 7 reaches diagonally below the flow rate reduction component. FIG. [Figure 10] 13 is a diagram for explaining the behavior of a fluid flowing through the first stage annular passage, and shows how air bubbles present in the stagnation region are discharged to the outside of the first stage outer cylinder through the opening. FIG. [Figure 11] FIG. 1 is a diagram showing the relationship between the quality at the inlet of a steam-water separator and the carry-under. [Figure 12] FIG. 4 is a partial cross-sectional view of a steam-water separator according to another embodiment. [Figure 13] FIG. 11 is an external view of a steam-water separator according to still another embodiment. [Figure 14] FIG. 14 is a vertical sectional view of the steam-water separator shown in FIG. [Figure 15] FIG. 15 is a cross-sectional view taken along the line DD in FIGS. 13 and 14. [Figure 16] 15 is a cross-sectional view taken along the line EE in FIG. 13 and FIG. 14. [Figure 17] 14 is a bird's-eye view of the vicinity of an opening of the steam-water separator shown in FIG. 13, as viewed from outside the steam-water separator. [Figure 18] 1 is a vertical cross-sectional view of a schematic structure of a boiling water reactor (forced circulation reactor) according to the present disclosure. [Figure 19] FIG. 2 is a vertical cross-sectional view showing a steam-water separator of a reference example. [Figure 20] FIG. 4 is a horizontal cross-sectional view showing a plurality of steam-water separators of a reference example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, a form for carrying out the present disclosure (referred to as an embodiment) will be described with reference to the drawings. In the following description of one embodiment, other embodiments applicable to the one embodiment will also be described as appropriate. The present disclosure is not limited to the following one embodiment, and different embodiments can be combined with each other or modified as desired without significantly impairing the effects of the present disclosure. In addition, the same symbols will be used for the same members, and duplicate descriptions will be omitted. Furthermore, the same names will be used for members having the same functions. The contents shown are merely schematic, and for the sake of illustration, changes may be made from the actual configuration within a range that does not significantly impair the effects of the present disclosure, and some members may be omitted or modified between drawings. In addition, the same embodiment does not necessarily need to have all the configurations.

[0011] FIG. 1 is a vertical cross-sectional view of a schematic structure of a boiling water reactor (natural circulation reactor) of the present disclosure. Hereinafter, the boiling water reactor (natural circulation reactor) of the present disclosure is abbreviated as a reactor 142. The reactor 142 is of a natural circulation type. Therefore, the reactor 142 does not include a recirculation pump 113 (described later), but includes a chimney 143. In the natural circulation path, the fluid 5 naturally circulates inside and outside the core 103 using the density difference of the fluid 5 inside and outside the core 103 as a driving force. The fluid 5 is mainly composed of liquid water 3 (coolant 118), or liquid water 3 and bubbles 6 (steam in water), as described later with reference to FIG. 7, for example. The natural circulation type can suppress the occurrence of cavitation in, for example, an impeller 177 (described later), etc.

[0012] The nuclear reactor 142 includes a reactor pressure vessel 101, a reactor core 103, and a steam-water separator 105. The reactor core 103 is provided in the reactor pressure vessel 101, and fuel assemblies are loaded therein. The steam-water separator 105 is provided in the reactor pressure vessel 101, and separates liquid water 3 and gas bubbles 6 from a fluid 5 consisting of gas bubbles 6 (steam) and liquid water 3, which is generated in the reactor core 103.

[0013] A cylindrical core shroud 102 is provided in a reactor pressure vessel 101, and a core 103 loaded with a plurality of fuel assemblies (not shown) is installed in the core shroud 102. An upper lattice plate 119 is installed at the upper end of the core 103 in the core shroud 102, and a chimney 143 is installed above that, and a core support plate 108 is installed at the lower end of the core in the core shroud 102. In addition, a plurality of fuel support brackets 109 are installed on the core support plate 108.

[0014] Further, within the reactor pressure vessel 101, there is provided a control rod guide tube 110 that enables a plurality of cross-shaped control rods (not shown) to be inserted into the core 103 in order to control the nuclear reaction of the fuel assemblies. A control rod drive mechanism 111 is provided within a housing installed below the bottom of the reactor pressure vessel 101, and the cross-shaped control rods are connected to the control rod drive mechanism 111. The coolant 118 flowing into the core 103 is heated by the nuclear reaction of the fuel assemblies and becomes a fluid 5 containing steam and water (a mixed flow of water 3 and gas bubbles 6), and the fluid 5 flows into a steam-water separator 105 disposed at the top of the core 103.

[0015] The fluid 5 flowing into the steam separator 105 is given a swirling speed by a swirler 122 (described later) in the steam separator 105, and centrifugal force acts on the fluid 5 due to the swirling speed, and the liquid water 3 and the gas bubbles 6 are separated due to the density difference between them, and the water 3 flows again to the downcomer 114 as a coolant 118. Meanwhile, the gas bubbles 6 flow into the steam dryer 106 as steam, where the moisture is further removed. In this way, the steam with a moisture content of 0.1 mass percent or less is sent to a turbine (not shown) through the main steam pipe 115, and power is generated. The coolant 118 flowing into the reactor pressure vessel 101 from the feedwater pipe 116 via a condenser or the like (not shown) flows downward in the downcomer 114, and flows into the core 103 due to a circulating force caused by the density difference between the fluid 5 inside and outside the core shroud 102. For example, outside the core 103, liquid water 3 is the main component and has a relatively high density, whereas inside the core 103, steam (bubbles 6) is the main component and has a relatively low density.

[0016] For convenience, a steam-water separator 1051 of a reference example will first be described with reference to Fig. 19 and Fig. 20. The steam-water separator 1051 of the reference example has the same structure as the steam-water separator 105 (described later) of the present disclosure, except that it is not provided with an opening 1 (described later). In the present disclosure, the steam-water separator 105, 1051 having two or more stages of separation mechanisms is preferable, and Fig. 19 and Fig. 20 show the steam-water separator 105, 1051 having a three-stage separation mechanism as an example. However, the steam-water separator 105, 1051 may be one or two stages, or four or more stages.

[0017] FIG. 19 is a vertical cross-sectional view showing a steam-water separator 1051 of a reference example. FIG. 19 is a cross-sectional view taken along line AA in FIG. 20 described later. The steam-water separator 1051 includes a standpipe 120 that guides a fluid 5 (a fluid including steam and water) generated in the core 103 (FIG. 1) from below to above. The steam-water separator 1051 includes a diffuser 121 that is connected to an upper end face of the standpipe 120 to form a flow path and expands the flow path cross-sectional area upward from the flow path cross-sectional area of ​​the upper end face. The steam-water separator 1051 includes a first stage inner cylinder 123 that communicates with an upper end of the diffuser 121 to form a flow path. The first stage inner cylinder 123 (inner cylinder), and the second stage inner cylinder 129 and the third stage inner cylinder 135 described later have a cylindrical shape.

[0018] The steam-water separator 1051 includes a first-stage annular flow passage 126 that surrounds the first-stage inner cylinder 123 at a concentric interval. The steam-water separator 1051 includes a first-stage outer cylinder 124 that forms a first-stage annular flow passage 126 (annular flow passage) between the first-stage inner cylinder 123 and the first-stage outer cylinder 124 and that includes a first-stage outlet 127 (outlet) that opens downward at the lower end of the first-stage annular flow passage 126. The first-stage outer cylinder 124, as well as a second-stage outer cylinder 130 and a third-stage outer cylinder 136 described below, have a cylindrical shape. The first-stage outer cylinder 124 is disposed opposite the first-stage inner cylinder 123 and the diffuser 121. The first-stage annular flow passage 126 formed between the first-stage inner cylinder 123 and the first-stage outer cylinder 124 opens downward, and the first-stage outlet 127 is formed downward. Therefore, the fluid 5 flowing downward in the first stage annular flow passage 126 is discharged downward as it is through the first stage discharge port 127 without changing its flow direction to the side.

[0019] The steam-water separator 1051 includes a flow rate reduction component 141 provided in the first stage annular flow passage 126. The flow rate reduction component 141 (an example of a protruding portion) is formed so as to protrude into the first stage annular flow passage 126 from at least one surface of the first stage outer cylinder 124 or the first stage inner cylinder 123. The degree of protrusion is not particularly limited, and for example, the flow passage cross-sectional area of ​​the first stage annular flow passage 126 can be locally protruded to be, for example, 30% or more and 70% or less (for example, 50%).

[0020] The flow rate reduction component 141 is provided to limit the flow rate of the fluid 5 (separated water) flowing into the first-stage annular flow passage 126. The flow rate reduction component 141 is a ring-shaped component in the illustrated example, but it is not an independent component and may be formed, for example, by the inner surface of at least one of the first-stage inner cylinder 123 or the first-stage outer cylinder 124. That is, a protruding portion may be formed by protruding at least a part (which may be the entire area) in the circumferential direction of at least one of the inner surfaces so that the flow passage cross-sectional area of ​​the first-stage annular flow passage 126 is locally smaller than other parts. In this case, the protruding portion is a part of at least one of the first-stage inner cylinder 123 or the first-stage outer cylinder 124.

[0021] The steam-water separator 1051 includes a first stage annular plate 128 (annular plate) that closes the upper side surface of the first stage outer cylinder 124 and has a circular hole formed therein with a smaller diameter than the first stage inner cylinder 123. The steam-water separator 1051 includes a first stage pick-off ring 125 (pick-off ring) that extends cylindrically downward from the inner circumferential edge of the first stage annular plate 128 that forms the circular hole, and forms the circular hole as a short flow path (a flow path upwardly of the first stage inner cylinder 123) to the second stage inner cylinder 129 and the second stage outer cylinder 130.

[0022] The steam-water separator 1051 includes a second stage inner cylinder 129 that is placed on the first stage annular plate 128 and forms a flow path. The steam-water separator 1051 includes a second stage annular flow path 132 that concentrically surrounds the second stage inner cylinder 129 with a gap therebetween. The steam-water separator 1051 includes a second stage outer cylinder 130 that is provided with a second stage outlet 133 below the second stage annular flow path 132. The steam-water separator 1051 includes a second stage annular plate 134 that closes the upper side surface of the second stage outer cylinder 130 and has a circular hole with a smaller diameter than the second stage inner cylinder 129 formed therein.

[0023] The steam-water separator 1051 includes a second-stage pick-off ring 131 that extends cylindrically downward from the inner circumferential edge of the second-stage annular plate 134 that forms the circular hole, forming a short flow passage to a third-stage inner cylinder 135 and a third-stage outer cylinder 136. The steam-water separator 1051 includes a third-stage inner cylinder 135 that is installed on the second-stage annular plate 134 and forms a flow passage. The steam-water separator 1051 includes a third-stage annular flow passage 138 that concentrically surrounds the third-stage inner cylinder 135 with a gap therebetween. The steam-water separator 1051 includes a third-stage outer cylinder 136 that provides a third-stage outlet 139 below the third-stage annular flow passage 138. The steam-water separator 1051 includes a third-stage annular plate 140 that closes the upper surface of the third-stage outer cylinder 136 and forms a circular hole with a smaller diameter than the third-stage inner cylinder 135.

[0024] The steam-water separator 1051 includes a third-stage pick-off ring 137 that extends cylindrically downward from the inner circumferential edge of the third-stage annular plate 140 that forms the circular hole, and forms the circular hole as an outlet flow passage of the steam-water separator 1051. The steam-water separator 1051 includes a hub 1222 that passes through the axial center of the flow passage of the fluid 5, and a plurality of swirl vanes 1221 that are attached radially around the hub 1222. The radially inner edge of the swirl vane 1221 is fixed to the hub 1222. The steam-water separator 1051 includes a swirler 122 that has a radially outer edge fixed to the inner wall of the diffuser 121 or the inner wall of the first-stage inner cylinder 123. The swirler 122 is disposed as the axial center of the flow passage through which the fluid 5 flows in the standpipe 120.

[0025] 20 is a horizontal cross-sectional view showing a plurality of steam-water separators 1051 of a reference example. In a nuclear reactor 142, a plurality of steam-water separators 1051 are arranged at regular intervals. A flow path 144 through which a fluid 5 flows is formed between the plurality of steam-water separators 1051.

[0026] Next, the steam-water separator 105 of the present disclosure will be described. As described above, the steam-water separator 105 further includes an opening 1 in the steam-water separator 1051 shown in Fig. 19. Therefore, the same reference numerals are used to denote the same members, and duplicated descriptions will be omitted.

[0027] Fig. 2 is an external view of the steam-water separator 105 of the present disclosure. Fig. 3 is a vertical cross-sectional view of the steam-water separator 105 shown in Fig. 2. Part of the structure of the steam-water separator 105 is omitted in Figs. 2 and 3. Fig. 4 is a cross-sectional view taken along line BB in Figs. 2 and 3. Fig. 5 is a cross-sectional view taken along line CC in Figs. 2 and 3. Fig. 6 is a bird's-eye view of the vicinity of the opening 1 of the steam-water separator 105 shown in Fig. 2, as viewed from the outside of the steam-water separator 105.

[0028] The water-steam separator 105 has an opening 1. The opening 1 is provided near a stagnation area S (described later) formed below a flow rate reduction component 141 (protrusion). The opening 1 discharges at least air bubbles 6 (steam; described later) in a fluid 5 flowing through the water-steam separator 105 (e.g., first-stage annular flow passage 126) to the outside of the first-stage outer casing 124. This makes it possible to reduce the amount of air bubbles 6 discharged through a first-stage outlet 127, which is the end point of the first-stage annular flow passage 126.

[0029] The fluid 5 (mainly water 3) discharged from the first stage outlet 127 reaches the downcomer 114. Therefore, if the amount of bubbles 6 in the fluid 5 reaching the downcomer 114 is large, the density of the fluid 5 decreases. As a result, the difference between the density of the fluid 5 in the downcomer 114 and the density of the fluid 5 inside the core 102 becomes relatively small, making it difficult for natural circulation to occur using the density difference. Therefore, by providing the opening 1, the amount of bubbles 6 discharged through the first stage outlet 127 can be reduced, and the density of the fluid 5 in the downcomer 114 can be relatively reduced. As a result, the difference between the density of the fluid 5 in the downcomer 114 and the density of the fluid 5 inside the core 102 can be increased. Therefore, it is possible to easily generate natural circulation using the density difference.

[0030] In the example of the present disclosure, the opening 1 discharges at least the air bubbles 6 present in the stagnation region S to the outside of the first stage external cylinder 124. However, the opening 1 may be formed in at least one of the second stage external cylinder 130 or the third stage external cylinder 136. In addition, the flow rate reduction component 141 may also be formed in at least one of the second stage external cylinder 130 or the third stage external cylinder 136.

[0031] The opening 1 is formed in the first stage external cylinder 124 at least in a portion directly below (directly below) the flow rate reduction component 141. The opening 1 communicates between the first stage annular flow path 126 and the outside of the first stage external cylinder 124, and opens toward a side of the first stage external cylinder 124. In other words, the opening 1 communicates between the inside and the outside of the steam-water separator 105. As shown in FIG. 4, in the example of the present disclosure, the flow rate reduction component 141 is in the shape of a ring provided over the entire circumferential area of ​​the first stage external cylinder 124.

[0032] 5 etc., a plurality of openings 1 are provided at regular intervals (equidistant intervals) in the circumferential direction of the first stage external cylinder 124. In addition, the flow rate reduction component 141 is provided over the entire circumferential area on the inner surface of the first stage external cylinder 124. Therefore, the openings 1 may be provided at any circumferential position.

[0033] The opening 1 has a shape in which the length in the circumferential direction of the first-stage outer cylinder 124 is longer than the length in the vertical direction. The vertical direction here refers to the extension direction of the first-stage inner cylinder 123, the first-stage outer cylinder 124, and the first-stage annular flow passage 126, and is the flow direction of the fluid 5 flowing through the first-stage annular flow passage 126. With the opening 1 having such a shape, many air bubbles 6 (described later) that have accumulated in a stagnation area S (described later) directly below the flow rate reduction component 141 can be discharged to the outside of the air-water separator 105.

[0034] The opening 1 has a trapezoidal shape expanding from the inside to the outside of the first stage outer cylinder 124 when viewed from the top of the first stage outer cylinder 124. Furthermore, the opening 1 has a rectangular shape (e.g., a rectangular shape) when viewed from the side of the first stage outer cylinder 124. However, the opening 1 may be a circle, an ellipse, a diamond shape, etc. In the case of a shape other than a rectangle, the vertical length of the opening 1 is the length of a line segment connecting the uppermost end and the lowermost end of the opening 1. Furthermore, in this case, the length of the opening 1 in the circumferential direction of the first stage outer cylinder 124 is the length of the part of the opening 1 that has the longest distance in the circumferential direction. Furthermore, the number of openings 1 may be only one or more.

[0035] 3, the opening 1 is formed above the upper end of the diffuser 121. As described above, the diffuser 121 expands the flow path cross-sectional area from the lower end of the diffuser 121 upward. Therefore, above the diffuser 121, the cross-sectional area of ​​the first stage annular flow path 126 at the portion where the opening 1 is located is relatively small. This increases the change in flow velocity caused by the flow rate reduction component 141, making it easier to accumulate a large number of bubbles in a stagnation region S (described later) below the flow rate reduction component 141. This makes it easier to discharge bubbles 6 (described later) from the stagnation region S through the opening 1.

[0036] The opening 1 is provided at a position facing the first stage annular flow path 126. By forming it at this position, air bubbles 6 in the fluid 5 that flows downward through the first stage annular flow path 126 and passes near the flow rate reduction component 141 can be easily retained in the stagnation region S below the flow rate reduction component 141. This makes it easier to discharge the air bubbles 6 to the outside of the air-water separator 105 through the opening 1.

[0037] The opening 1 directly faces at least one surface (surface on the first-stage outer cylinder 124 side) of the first-stage inner cylinder 123, the diffuser 121, or the stand pipe 120. This allows the opening 1 to be directly exposed to the first-stage annular flow passage 126, so that the bubbles 6 can be separated, so to speak, from the fluid 5 flowing through the first-stage annular flow passage 126, and can be easily retained in the stagnation region S. In the illustrated example, the opening 1 directly faces the side surface of the first-stage inner cylinder 123.

[0038] The significance of providing the opening 1 will be explained below.

[0039] FIG. 7 is a diagram for explaining the behavior of the fluid 5 flowing through the first-stage annular flow passage 126, focusing on specific bubbles 6 in the first-stage annular flow passage 126. The fluid 5 is composed of liquid water 3 and bubbles 6. In FIG. 7 and FIGS. 8 to 10 described later, only local bubbles 6 are illustrated, but in reality, bubbles 6 may exist throughout the entirety or part of the first-stage annular flow passage 126. When the quality at the inlet (the lower end of the standpipe 120) of the steam separator 105 is high, that is, when the amount of steam is large, bubbles 6 (steam) flow from above into the first-stage annular flow passage 126 together with liquid water 3 (separated water), as shown in FIG. 7.

[0040] Fig. 8 is a diagram for explaining the behavior of the fluid 5 flowing through the first-stage annular flow passage 126, and is a diagram showing the state when the air bubble 6 shown in Fig. 7 flows near the flow rate reduction component 141. At the height position where the flow rate reduction component 141 is installed in the first-stage annular flow passage 126, as shown by the thick solid arrow, the flow passage becomes narrower and the downward flow rate is faster than the flow rate in other regions shown by the thin solid arrows. Therefore, the flow rate of the air bubble 6 becomes locally faster on the side of the flow rate reduction component 141 (part where the flow passage cross-sectional area is locally smaller).

[0041] 9 is a diagram for explaining the behavior of the fluid 5 flowing through the first stage annular flow path 126, and shows the state when the air bubble 6 shown in FIG. 7 above reaches diagonally below the flow rate reduction component 141. A downward flow is generated from the flow of the fluid 5 that has passed beside the flow rate reduction component 141, and a stagnation region S where the water flow stagnates due to being drawn in directly below the flow rate reduction component 141 is generated.

[0042] In addition, the flow rate decreases as the flow path widens. According to the inventors' study, when the speed (steam speed) of the bubbles 6 is calculated from the steam flow rate flowing into the first stage annular flow path 126 and the flow path area after passing through the height position where the flow rate reduction component 141 is installed, the speed of the bubbles 6 is a very slow flow rate, for example, less than 1 m / s. Furthermore, as a result of studying the magnitude relationship between the drag force trying to flow the bubbles 6 downward and the buoyancy of the bubbles 6, it was confirmed that the buoyancy is larger. Therefore, due to the buoyancy generated in the bubbles 6, the bubbles 6 contained in the fluid 5 are unlikely to flow downward as is, and are likely to accumulate in the stagnation area S directly below the flow rate reduction component 141.

[0043] 10 is a diagram for explaining the behavior of the fluid 5 flowing through the first-stage annular flow passage 126, and shows how the air bubbles 6 present in the stagnation region S are discharged to the outside of the first-stage outer cylinder 124 through the opening 1. The air bubbles 6 accumulated in the stagnation region S are discharged from the opening 1 together with the liquid water 3. The discharged air bubbles 6 rise through the above-mentioned flow passage 144. This makes it possible to prevent the air bubbles 6 from flowing into the downcomer 114.

[0044] In the example of the present disclosure, the lower surface of the flow rate reduction component 141 (the surface facing the opening 1) extends horizontally. However, the lower surface may have a slope such that the height position of the end portion closer to the opening 1 becomes relatively higher from the end portion farther from the opening 1 (the left end portion in the illustrated example) toward the end portion closer to the opening 1 (the right end portion in the illustrated example). This makes it easier for the air bubbles 6 to flow into the opening 1.

[0045] 11 is a diagram showing the relationship between quality and carry-under at the inlet of the steam-water separator 105. The solid line is the performance curve of the steam-water separator 105 of the present disclosure, and the dashed line is the performance curve of a conventional steam-water separator (Patent Document 1).

[0046] The horizontal axis represents the quality at the inlet of the steam-water separator 105 (the inlet of the standpipe 120), and the vertical axis represents the carry-under. The quality is the ratio of the steam mass flow rate to the total mass flow rate at the inlet of the steam-water separator 105, and it can be said that the higher the quality, the greater the amount of steam supplied. Therefore, high quality is preferable. At the top of the graph, the quality ranges targeted by this disclosure (solid line) and the conventional method (dashed line) are shown.

[0047] Carry under refers to the occurrence of cavitation that may occur in the recirculation pump 113 (described later) or the like. In the case of a nuclear reactor 142 that does not have a recirculation pump 113, the occurrence of cavitation is unthinkable. However, when there are so many bubbles 6 that cavitation occurs, the density difference of the fluid 5 inside and outside the core 103 becomes small, and natural convection is difficult to occur. In other words, the fluid 5 is difficult to flow. Therefore, in order to evaluate the difficulty (ease of flow) of the fluid 5 to flow, the concept of carry under, which assumes the occurrence of cavitation, is used even in a nuclear reactor 142 that does not have a recirculation pump 113.

[0048] 11 is a mass flow rate ratio that causes a carry-under among the mass flow rate ratio of the bubbles 6 in the fluid 5 discharged from the discharge flow passage (first stage outlet 127) of the steam-water separator 105. Therefore, the nuclear reactor 142 is operated at a mass flow rate ratio that causes a carry-under or less.

[0049] For the conventional steam-water separator (dashed line), the quality range is narrow from A0 to A1, and the carry-under B0 of the quality A1 satisfies the conventional limit value B1. The limit value B1 is the upper limit of the operating conditions that do not cause carry-under. On the other hand, for the steam-water separator 105 of the present disclosure, the quality range is wide from A0 to A2, and the carry-under of the quality A2 is B1. That is, in the steam-water separator 105 of the present disclosure, the air bubbles 6 are discharged from the opening 1, so that the amount of the air bubbles 6 in the fluid 5 discharged from the outlet (first-stage outlet 127) of the steam-water separator 9 is reduced. Therefore, the carry-under of the quality A2 can be reduced from the conventional B2 to B1.

[0050] 12 is a partial cross-sectional view of a steam-water separator 105 of another embodiment. In the steam-water separator 105 shown in FIG. 12, at least the upper part 11 of the inner surface forming the opening 1 has a slope that rises from the inside to the outside of the first-stage external cylinder 124. That is, the height position of the opening on the outer surface of the first-stage external cylinder 124 is higher than the opening on the inner surface of the first-stage external cylinder 124. These two openings form the opening 1. Since the air bubbles 6 are lighter (have a lower density) than water, the air bubbles 6 that reach the inside of the opening 1 from the stagnation region S reach the upper part 11 side rather than the lower part 12. Therefore, the air bubbles 6 can be easily discharged to the outside inside the opening 1 along the slope that rises outward.

[0051] In the example of the present disclosure, at least the lower portion 12 of the inner surface forming the opening 1 also has an upward inclination from the inside to the outside of the first stage outer cylinder 124. Therefore, the opening 1 has a box-like shape having an upward inclination from the inside to the outside of the first stage outer cylinder 124.

[0052] Fig. 13 is an external view of a steam-water separator 105 of still another embodiment. Fig. 14 is a vertical sectional view of the steam-water separator 105 shown in Fig. 13. Part of the structure of the steam-water separator 105 is omitted in Figs. 13 and 14. Fig. 15 is a sectional view taken along line DD in Figs. 13 and 14. Fig. 16 is a sectional view taken along line EE in Figs. 13 and 14. Fig. 17 is a bird's-eye view of the vicinity of the opening 1 of the steam-water separator 105 shown in Fig. 13, as viewed from the outside of the steam-water separator 105. The explanation of the opening 1 shown in Figs. 2 to 6 above can be similarly applied to the opening 1 shown in Figs. 13 to 17, except for the matters described below.

[0053] In the steam-water separator 105 shown in Figs. 13 to 17, the opening 1 has a shape in which the length in the circumferential direction of the first-stage outer cylinder 124 is shorter than the length in the vertical direction. This allows the air bubbles 6 that have flowed from the flow rate reduction component 141 toward the first-stage outlet 127 to a location away from the flow rate reduction component 141 to be discharged through the opening 1. In particular, when the flow velocity of the fluid 5 flowing through the first-stage annular flow path 126 is relatively fast, the vertical length of the stagnation region S becomes relatively longer than when the flow velocity is relatively slow. For this reason, by providing such an opening 1, it is possible to suppress "leaking" of the air bubbles 6.

[0054] The opening 1 has a vertically long flat shape. However, the opening 1 may also be a vertically long rectangular shape. Furthermore, a plurality of openings 1 are provided at equal intervals in the circumferential direction of the first stage outer cylinder 124. In the illustrated example, the lower end of the opening 1 is at the same height as the lower end of the diffuser 121, but may be at a higher position than the lower end of the diffuser 121 or at a lower position than the lower end of the diffuser 121.

[0055] 18 is a vertical cross-sectional view of a schematic structure of a boiling water reactor (forced circulation reactor) of the present disclosure. Hereinafter, the boiling water reactor (forced circulation reactor) of the present disclosure is abbreviated as reactor 145. In the present disclosure, the natural circulation type reactor 142 is preferred, but a forced circulation type reactor 145 may also be used. The reactor 145 includes a recirculation pump 113 that forcibly circulates the fluid 5 inside the reactor pressure vessel 101. However, unlike the reactor 142, the chimney 143 (FIG. 1) is not included.

[0056] The recirculation pump 113 is an internal pump that circulates the fluid 5 inside and outside the reactor core 103, and includes an impeller 117. By being driven by the impeller 117, the fluid 5 can be forced to flow through the first stage annular flow passage 126, the second stage annular flow passage 132, and the third stage annular flow passage 138.

[0057] In the reactor 145, it is preferable to drive the recirculation pump 113 so as to achieve a flow rate at which the bubbles 6 present in the stagnation region S can be discharged through the opening 1. In particular, since the slower the flow rate, the more the bubbles 6 are promoted to be discharged through the opening 1, it is preferable to drive the recirculation pump 113 so as to slow the flow rate in the reactor 145 as well. This makes it possible to sufficiently avoid carry-under. [Explanation of symbols]

[0058] 1 Opening 10 Stagnation area 101 Reactor Pressure Vessel 102 Core Shroud 103 Core 105 Steam water separator 1051 Steam water separator 106 Steam dryer 108 Core Support Plate 109 Fuel support bracket 11 Top 110 Control rod guide tube 111 Control Rod Drive Mechanism 113 Recirculation Pump 114 Down Cam 115 Main steam pipe 116 Water Supply Pipe 117 Impeller 118 Coolant 119 Upper grid plate 12 Upper part 120 Standpipe 121 Diffuser 122 Swara 1221 Swirling blade 1222 Hub 123 First stage inner cylinder (inner cylinder) 124 First stage outer cylinder (outer cylinder) 125 First stage pick-off ring (pick-off ring) 126 First stage annular passage (annular passage) 127 First stage discharge port (discharge port) 128 First stage annular plate (annular plate) 141 Flow reduction parts (protrusions) 142 Nuclear reactor 143 Chimney 144 Flow Path 145 Nuclear reactor 177 Impeller 3. Liquid Water 5 fluid 6. Bubbles 9 Steam water separator S stagnation area

Claims

1. A standpipe that guides fluids consisting of steam and water generated in the reactor core from below to above; a diffuser connected to an upper end of the standpipe to form a flow passage and having a flow passage cross-sectional area that is expanded upward from the flow passage cross-sectional area of ​​the upper end; a cylindrical inner tube that communicates with an upper end of the diffuser and forms a flow path; a cylindrical outer cylinder that forms an annular flow passage between the outer cylinder and the inner cylinder and that has a discharge port that opens downward at a lower end of the annular flow passage; a protrusion formed so as to protrude into the annular flow path from at least one surface of the outer cylinder or the inner cylinder; an opening formed in the outer cylinder at least directly below the protruding portion, the opening communicating the annular flow path with the outside of the outer cylinder and opening toward a side of the outer cylinder; an annular plate that closes an upper surface of the outer cylinder and has a circular hole with a diameter smaller than that of the inner cylinder; a pick-off ring extending cylindrically downward from an inner circumferential edge of the annular plate that defines the circular hole, and defining the circular hole as a flow passage upward in the inner cylinder; a swirler disposed at the axial center of a flow path through which the fluid flows in the standpipe; A steam-water separator characterized by:

2. The opening has a shape in which the length in the circumferential direction of the outer cylinder is longer than the length in the vertical direction.

2. The steam-water separator according to claim 1 .

3. The opening has a shape in which the length in the circumferential direction of the outer cylinder is shorter than the length in the vertical direction.

2. The steam-water separator according to claim 1 .

4. At least an upper portion of the inner surface forming the opening has an upward inclination from the inside to the outside of the outer cylinder.

2. The steam-water separator according to claim 1 .

5. the outer cylinder is disposed opposite the inner cylinder and the diffuser, The opening is formed above the upper end of the diffuser.

2. The steam-water separator according to claim 1 .

6. The opening is Discharging at least the steam to the outside of the outer cylinder; The annular flow passage is provided at a position facing the annular flow passage.

2. The steam-water separator according to claim 1 .

7. The opening is directly opposite a surface of at least one of the inner cylinder, the diffuser, or the standpipe.

7. The steam-water separator according to claim 6.

8. A reactor pressure vessel; a reactor core provided within the reactor pressure vessel and loaded with fuel assemblies; a steam-water separator provided in the reactor pressure vessel and configured to separate the liquid water and the steam from a fluid consisting of the steam and liquid water generated in the reactor core; The steam-water separator comprises: a standpipe for guiding the fluid generated in the core from below to above; a diffuser connected to an upper end of the standpipe to form a flow passage and having a flow passage cross-sectional area that is expanded upward from the flow passage cross-sectional area of ​​the upper end; a cylindrical inner tube that communicates with an upper end of the diffuser and forms a flow path; a cylindrical outer cylinder that forms an annular flow passage between the outer cylinder and the inner cylinder and that has a discharge port that opens downward at a lower end of the annular flow passage; a protrusion formed so as to protrude into the annular flow path from at least one surface of the outer cylinder or the inner cylinder; an opening formed in the outer cylinder at least directly below the protruding portion, the opening communicating the annular flow path with the outside of the outer cylinder and opening toward a side of the outer cylinder; an annular plate that closes an upper surface of the outer cylinder and has a circular hole with a diameter smaller than that of the inner cylinder; a pick-off ring extending cylindrically downward from an inner circumferential edge of the annular plate that defines the circular hole, and defining the circular hole as a flow passage upward in the inner cylinder; a swirler disposed at the axial center of a flow path through which the fluid flows in the standpipe; 1. A boiling water reactor comprising:

9. It is a natural circulation boiling water reactor.

9. The boiling water reactor of claim 8.

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